1. Field of the Invention
The present invention is directed to an apparatus and method for impregnating fiber bundles with powder materials. The method and apparatus are especially useful for providing uniform impregnation of carbon fiber tow bundles with low solubility, high melt flow polymer powder materials to produce composite prepregs. Improved materials such as high temperature and high modulus reinforced thermoplastics may be obtained by the method and apparatus of the invention.
2. Description of the Related Art
Impregnation of materials, for example for the production of prepregs, has been accomplished by solvent, slurry and film coating techniques. These techniques require the removal of solvents and/or carrier materials or require melt infusion of film into the material to produce prepregs. The removal of solvents and carrier materials to acceptable levels and total infiltration of fiber bundles with polymer films each have proven to be significant barriers to the production of high quality uniformly impregnated prepregs.
U.S. Pat. No. 4,735,858 to Hosokawa et al discloses a prepreg which is heat resistant. The prepreg is obtained by impregnating a heat-resistant substrate with a heat-resistant mixture as a matrix, and subjecting the resulting impregnated product to heat. The substrate may be of liquid crystal fibers, carbon fibers, inorganic fibers, metallic fibers, and mixed fibers thereof. The substrate may be in the form of threads, non-woven fabrics, woven fibers and papers. The heat-resistant mixture is formed by dissolving component materials in solvent, and is impregnated into the substrate by conventional methods.
U.S. Pat. No. 4,211,818 to Ackley discloses composite strands of resin, carbon and resin sheets reinforced by glass and carbon strands. The composite strands are wetted by resin in a bath and formed by passing the strands through a die as they emerge from the bath to control their resin content.
As an alternative to using solvents, fluidized beds may be provided. Fluidized beds permit the suspension and maintenance of solid material in a finely divided form in a state of turbulent motion in a stream of gas. The surface activity of the particles is increased by fluidizing. However, the particles are merely coated onto a surface of an article, and are unable to penetrate within the article.
The above methods of impregnation require impregnation by liquids for preparation, or merely coat an article. However, the use of liquids has proven to be undesirable, especially with impregnating materials which are insoluble in any solvent or insoluble in few solvents. Further, fluidized beds are incapable of impregnating materials into an article. Accordingly, it is desirable to provide a method and apparatus for impregnating materials which do not require liquids for their operation.